Inorg. Chem. 2002, 41, 492−500 Chalcogen-Rich Lanthanide Clusters: Compounds with Te2-, (TeTe)2-, 5- 9- TePh, TeTePh, (TeTeTe(Ph)TeTe) , and [(TeTe)4TePh] Ligands; Single Source Precursors to Solid-State Lanthanide Tellurides Deborah Freedman, Thomas J. Emge, and John G. Brennan* Department of Chemistry, Rutgers, the State UniVersity of New Jersey, 610 Taylor Road, Piscataway, New Jersey 08854-8087 Received September 19, 2001 Lanthanide metals react with PhTeTePh and elemental Te in pyridine to give (py)yLn4(Te)(TeTe)2(TeTeTe(Ph)- TeTe)(TexTePh) (Ln ) Sm (y ) 9; x ) 0); Tb, Ho (y ) 8, x ) 0.1)), and (py)7Tm4(Te)[(TeTe)4TePh](Te0.6TePh) clusters. The Sm, Tb, and Ho compounds contain a square array of Ln(III) ions all connected to a central Te2- ligand. Two adjacent edges of the square are bridged by ditelluride ligands, with the Ln ion that is η2 bound to both of these TeTe ligands also coordinating to a terminal TePh ligand. The other two edges of the square are spanned by ditellurides that both coordinate a TePh ligand that has been displaced from the Ln ion by pyridine, to give the 2 2 5- pentaanion (µ-η -η -Te2Te(Ph)Te2). In the Tm compound, the displaced TePh interacts with all four TeTe units. The compounds are air-, light-, and temperature-sensitive. Upon thermolysis, they decompose to give solid-state TbTe2-x, HoTe, or TmTe, with elimination of Te and TePh2. Introduction energy surfaces, and the combination of ionic Ln metal and covalent Te ligands yields compounds that are particularly Inorganic compounds of tellurium are challenging syn- difficult to isolate and characterize. This is reflected in the thetic targets, because bonds to this element are considerably literature, where over a hundred examples of structurally weaker than bonds to the lighter chalcogens sulfur or se- characterized compounds containing Ln-S bonds, more than lenium, and thus, compounds are relatively unstable. Because 35 examples of compounds with Ln-Se bonds, and only 12 this relative instability often leads to the formation of ma- analogous Ln-Te compounds have been described.3 A terials with highly unusual or useful physical properties (i.e., - 1 2 majority of the 12 Ln Te compounds contain relatively CdHgTe semiconductors, Bi Te thermoelectric materials ), - 2 3 electronegative, sterically demanding ancillary ligands4 7 the chemistry of metal tellurium compounds continues to (i.e., C Me or Cp*) that kinetically passivate the Ln-Te attract attention. From a fundamental perspective, compounds 5 5 bond. Most of the remaining examples are divalent Ln(ER) with Te are interesting because they often adopt unconven- 2 coordination complexes of the redox active Sm, Eu, or tional molecular or solid-state structures with a wide range - Yb.8 10 The tendency of the trivalent redox active metals to of Te-Te bonds, a chemistry that parallels that of the com- reductively eliminate RTeTeR clearly reflects the inability plex polyiodide compounds. Stabilities are defined by shal- of Te ligands to stabilize Ln(III) oxidation states. In the low potential energy surfaces, and structures are often un- absence of stabilizing ancillary anions, the only reported predictable. example of an isolable Ln(III)-Te compound is (Me2PCH2- Lanthanide (Ln) ions, with their valence 4f obitals ef- fectively shielded by filled 5s2 and 5p6 orbitals, also tend to (3) Nief, F. Coord. Chem. ReV. 1998, 178, 13. adopt molecular structures defined by shallow potential (4) Berg, D.; Andersen, R. A.; Zalkin, A. Organometallics, 1988, 7, 1858. (5) Evans, W. J.; Rabe, G. W.; Ziller, J. W.; Doedens, R. J. Inorg. Chem. 1994, 33, 2719. * Author to whom correspondence should be addressed. E-mail: bren@ (6) Zalkin, A.; Berg, D. Acta Crystallogr. 1988, C44, 1488. rutchem.rutgers.edu. (7) Recknagel, A.; Noltemeyer, M.; Stalke, D.; Pieper, U.; Schmidt, H. (1) Andresen, B. F.; Scholl, M. S., Eds. Infrared Technology and G.; Edelmann, F. T. J. Organomet. Chem. 1991, 411, 347. Applications XXIV; SPIE Proceedings Vol. 3436, San Diego, CA, (8) Khasnis, D. V.; Lee, J.; Brewer, M.; Emge, T. J.; Brennan, J. G. J. 1998. Am. Chem. Soc. 1994, 116, 7129. (2) Mathiprakasam, B.; Heenan, P., Eds., Proceedings of the Thirteenth (9) Brewer, M.; Khasnis, D.; Buretea, M.; Berardini, M.; Emge, T. J.; International Conference on Thermoelectrics; AIP Conference Pro- Brennan, J. G. Inorg. Chem. 1994, 33, 2743. ceedings 316, Midwest Research Institute, 1995. (10) Cary, D. R.; Arnold, J. Inorg. Chem. 1994, 33, 1791. 492 Inorganic Chemistry, Vol. 41, No. 3, 2002 10.1021/ic010981w CCC: $22.00 © 2002 American Chemical Society Published on Web 01/11/2002 Chalcogen-Rich Lanthanide Clusters 11,12 R CH2PMe2)2La(TeSi(SiMe3)3)3. Without this chelating tometer with Cu K radiation. GCMS data were collected on a phosphine ligand, the analogous Ce derivative, “Ce(TeSi- 5890 Series II gas chromatograph with an HP 5971 mass selective detector. (SiMe3)3”, decomposes below room temperature to give the 11,12 equally unstable tellurido cluster Ce5Te3(TeSi(SiMe3)3)9. Synthesis of (py)9Sm4(µ4-Te)(µ2-TeTe)2(µ2-TeTeTe(Ph)TeTe)- · While the past three years has experienced a burst of (TePh) 5py (1). Samarium metal (0.30 g, 2.0 mmol) and Hg (0.05 activity describing the synthesis and characterization of stable g, 0.25 mmol) were added to a solution of diphenyl ditelluride (0.82 g, 2.0 mmol) in pyridine (50 mL). The reaction flask was wrapped lanthanide clusters coordinated to chalcogenido (E2-,E) 13-18 in aluminum foil up to the stopper. The next day elemental tellurium S, Se) ligands, extension of this work to compounds of was added (0.38 g, 3.0 mmol) to the yellow solution and unreacted Te has not yet appeared. The recent high-yield synthesis of Sm. The following day the solution was dark red, and a brick red 2- 19,20 chalcogen-rich Ln compounds with (EE) ligands, rather solid had precipitated. The solution was filtered and layered with - than E2 ligands, from the reactions of lanthanide chalco- 20 mL of hexanes to give dark red needles (100 mgs, 10%) that genolates with elemental E, leads to the suggestion that could be separated by hand from the dark solid major product. 2- 2- (EE) may stabilize Ln ions more effectively than E , pos- Synthesis of (py)8Tb4(µ4-Te)(µ2-TeTe)2(µ2-TeTeTe(Ph)TeTe)- sibly to the extent that compounds with Te can be isolated (Te0.1TePh)·4.5py (2). Terbium metal (0.32 g, 2.0 mmol) and Hg routinely. This paper outlines initial investigations into the (0.05 g, 0.25 mmol) were added to a solution of diphenyl ditelluride synthesis, characterization, stability, and thermolysis of Te- (0.82 g, 2.0 mmol) in pyridine (50 mL). The flask was wrapped in rich Ln clusters. aluminum foil. After stirring for 1 day, elemental tellurium (0.38 g, 3.0 mmol) was added to the dark golden brown mixture that Experimental Section still contained unreacted Tb. Two days later the metal had been consumed and there was a significant amount of dark red precipitate. General Methods. All syntheses were carried out under ultrapure The flask was heated to between 60 and 75 °Cforca.1htodissolve nitrogen (JWS), using conventional drybox or Schlenk techniques. the red solid. The red solution was filtered into a flask with either Solvents (Fisher) were refluxed continuously over molten alkali a flat bottom (modified Erlenmeyer) or a large round-bottom and metals or K/benzophenone and collected immediately prior to use. concentrated by ca. 3 mL. Hexanes (ca. 8 mL) were added rapidly Anhydrous pyridine (Aldrich) was purchased and refluxed over into the solution that was then re-covered with aluminum foil and KOH. PhTeTePh was prepared according to literature procedures.21 allowed to stand at rt for 2 days to give deep red crystals (0.34 g, Ln and Hg were purchased from Strem. Melting points were taken 35%) that were washed with hexane (5 mL) and did not decompose in sealed capillaries and are uncorrected. IR spectra were recorded or melt below 300 °C. Anal. Calcd for C64.5H62.5N10.5Tb4Te11.1:C, - on a Mattus Cygnus 100 FTIR spectrometer from 4000 to 600 cm 1 25.5; H, 2.07; N, 4.84. Found: C, 25.3; H, 2.19; N, 4.33. IR: 3077 as Nujol mulls on NaCl plates. Electronic spectra were recorded (m), 2933 (s), 2856 (s), 1630 (w), 1597 (s), 1580 (s), 1481 (m), on a Varian DMS 100S spectrometer with the samples in a 0.10 1465 (s), 1437 (s), 1384 (s), 1218 (m), 1145 (w), 1068 (m), 1038 mm quartz cell attached to a Teflon stopcock. Elemental analyses (m), 1030 (m), 1004 (m), 991 (m), 825 (w), 745 (s), 732 (w), 702 were performed by Quantitative Technologies, Inc. (Whitehouse (s), 623 (w), 602 (m), 451 (w), 405 (w) cm-1. Magnetic susceptibil- NJ). These compounds are sensitive to the thermal dissociation of ity: µeff (5-250 K) ) 7.87 (500 G); 7.91 (10 kG). The compound neutral donor ligands at room temperature, so the experimentally does not show an absorption maximum from 350 to 800 nm in determined elemental analyses are often found to be lower than THF. No 1H NMR resonances were detected in either THF or the computed analyses. The reported values were closest to the pyridine. Thermolysis: 100 mg of 1 was placed in a quartz tube calculated values, but analytical determinations gave a range of under vacuum for 5 min. The tube was then sealed and the sample values that were usually consistent with the one of the three unit temperature was increased at the rate of 20 °C/min with one end cell formulations described below.